I have thought about Miles and More for Europe and getting a Singapore Airlines card for Asia. The problem is more cards... I do not like having a lot of cards. Another issue is the taxes that you pay on Miles and More flights out of Europe.
I use my miles for long-haul flights First Class and I have been using United for hotels as well. They have had really good deals, especially last minute.
The ultimate would be one card for Air Travel, one card for hotels, but I just do not see that option out there right now.